The present invention relates to an optical switch, and in particular to an optical switch arranged to provide a copy of the optical signal being switched.
Many industries utilise optical switches in their equipment. For instance, the telecommunications industry utilises optical switches in optical dedicated protection and optical shared protection rings (OSPR""s). Optical transmission systems are often constructed with a fault recovery mechanism so that if there is a complete loss of transmission capability due to component and/or transmission line failure, the traffic can be reallocated to other physically diverse routes. Pending U.S. application Ser. No. 09/349,349 (incorporated herein by reference) describes such as OSPR system.
Switches are commonly incorporated in OSPR""s at network nodes. At a network node, a 2xc3x972 switch may be utilised to connect between working and protect transmitters/receivers and working and protect transmission lines. Although the OSPR is designed with a fault recovery mechanism, performance of the node will be seriously affected if a switch fails, or has to be removed for maintenance or in order to be replaced. In such an instance, switch failure maintenance can interrupt both working and protection traffic.
FIG. 1 shows a working (2) and protect (4) transmission line connected to respective working and protect receivers (6,8) via a 2xc3x972 switch (10). Similarly, the working and protect transmission lines (2xe2x80x2,4xe2x80x2) may be connected to the working and protect transmitters (6xe2x80x2,8xe2x80x2) via a 2xc3x972 switch (10xe2x80x2). Alternatively, a bi-directional 2xc3x972 switch and a combination transmitter/receiver can be used before the outgoing and incoming paths are routed to transmitter and receiver respectively. This allows these two switches to be combined into one (not shown).
A 2xc3x972 switch allows independent connection of working and protection optical channels (or transmission lines) to working or protection receiver or transmitter as appropriate. This functionality is required in both 1+1 (in which the same data is simultaneously transmitted along both the working and protection lines, providing redundancy in the event of either of the lines failing) and 1:1 protection switching (in which high priority data is typically transmitted along the working line, low priority data along the protect line; in the event of the working line failing, the high priority data is routed along the protect line).
FIG. 2 shows how such bi-directional 2xc3x972 switches may be incorporated into an OSPR module 20, which includes an optical cross connect (Oxc3x97C) 22. The Oxc3x97C contains optical switches to route traffic off and on the shared protection as described in U.S. application Ser. No. 09/349,349. An OSPR will be comprised of a number of such modules or nodes.
The above description is merely an example of how such an optical switch can be used. Many systems, not limited to telecommunications may utilise such optical switching arrangements. The failure of a switch, or a part of the switch, inevitably affects connectivity between the inputs and outputs, as does removal of the switch for repair or maintenance.
In a first aspect, the present invention provides an optical switch comprising two segments at least partially separated by a surface that is partially reflective and partially transmissive to optical signals being switched, each segment having at least one optical input and at least one optical output, the segments being arranged such that an optical signal can be switched from said input to said output by reflection from said surface, with the optical signal that is generated by transmission through said surface being directed to an output of the other segment.
Thus a copy of an incident optical signal can be automatically generated by the switch. This allows fast end to end protection to continue to operate in the presence of multiple failures of the network e.g. the failure of more than one path within the network. If an output fails, then the copy of the signal is already provided to another output for onward transmission.
Preferably each segment comprises a plurality of said inputs and a plurality of said outputs.
Preferably said surface is substantially 50% reflective and 50% transmissive in respect of the wavelength of the optical signal being switched. Thus incident signals will be split into two roughly equal components.
Preferably the switch further comprises beam steering means arranged to controllably switch the optical signal from said inputs to said outputs. Thus the optical signal may be re-directed within the switch as desired e.g. to different outputs or beam stops.
Preferably each segment further comprises electrical control means arranged to control the operation of the switch, with each segment being electrically separate. By having electrically separate segments, a failure of the electrical control means to one segment need not affect the functionality of the other segments.
Preferably the switch includes at least one optically amplifying region arranged to amplify optical signals within said switch. Thus attenuation in the switch can be at least partially compensated for.
Preferably said amplifying region is coupled to said surface so as to amplify optical signals being transmitted through said surface. For instance, the surface or window could be at least in part formed as a slab of amplifying material. Such a slab could form the window, or be part of a more complex structure forming the window e.g. a planar waveguide. Alternatively, one or more amplifying regions could be located elsewhere within the switch e.g. coupled to an input or an output.
Preferably the input and output positions of one of the segments are substantially the mirror image of the input and output positions of the second segment. This permits a relatively simple, reciprocal structure of the switch. If such a structure is not utilised, further internal optical beam directing means such as mirrors or waveguides may be required to direct the internal signals to the desired output.
In another aspect the invention provides a telecommunications network arranged to transmit optical signals comprising a switch.
Preferably the network includes at least one working and one protect channel each arranged to carry optical signals, with the optical signal of the working channel being input to the first segment of the switch, and the protect channel being input to the other segment.
In another aspect the present invention provides a telecommunications network arranged to transmit optical signals and comprising a plurality of switches as claimed in claim 1, wherein said switches are arranged to provide ladder type protection.
In a further aspect the present invention provides a computer program arranged to control the operation of a switch.
In another aspect the present invention provides a segment for an optical switch comprising a surface that is partially reflective and partially transmissive, the segment comprising at least one input and at least one output and being arranged to transmit optical signals from said input to said output by reflection from the surface.
In a further aspect the present invention provides method of switching an optical signal from at least one input to at least one output by reflecting the signal from a surface that is partially transmissive and partially reflective, with a portion of the optical signal that is transmitted through the surface being directed to a further output.